The telecommunications industry is in the process of developing a new generation of flexible and affordable communications that includes high-speed access while also supporting broadband services. Many features of the third generation (3G) mobile telecommunications system have already been established, but many other features have yet to be perfected. The Third Generation Partnership Project (3GPP) has been pivotal in these developments.
One of the systems within the third generation of mobile communications is the Universal Mobile Telecommunications System (UMTS) which delivers voice, data, multimedia, and wideband information to stationary as well as mobile customers. UMTS is designed to accommodate increased system capacity and data capability. Efficient use of the electromagnetic spectrum is vital in UMTS. It is known that spectrum efficiency can be attained using frequency division duplex (FDD) or using time division duplex (TDD) schemes. Space division duplex (SDD) is a third duplex transmission method used for wireless telecommunications.
As can be seen in FIG. 1, the UMTS architecture consists of user equipment 102 (UE), the UMTS Terrestrial Radio Access Network 104 (UTRAN), and the Core Network 126 (CN). The air interface between the UTRAN and the UE is called Uu, and the interface between the UTRAN and the Core Network is called Iu.
High-Speed Downlink Packet Access (HSDPA) and High-Speed Uplink Packet Access (HSUPA) are further 3G mobile telephony protocols in the High-Speed Packet Access (HSPA) family. They provide a smooth evolutionary path for UMTS-based networks allowing for higher data transfer speeds.
Evolved UTRAN (EUTRAN) is a more recent project than HSPA, and is meant to take 3G even farther into the future. EUTRAN is designed to improve the UMTS mobile phone standard in order to cope with various anticipated requirements. EUTRAN is frequently indicated by the term Long Term Evolution (LTE), and is also associated with terms like System Architecture Evolution (SAE). One target of EUTRAN is to enable all internet protocol (IP) systems to efficiently transmit IP data. The system will have only use a PS (packet switched) domain for voice and data calls, i.e. the system will contain Voice Over Internet Protocol (VoIP).
Information about LTE can be found in 3GPP TS 36.300 (V8.0.0, March 2007), Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)—Overall description; Stage 2 (Release 8), which is incorporated herein by reference in its entirety. UTRAN and EUTRAN will now be described in some further detail, although it is to be understood that especially E-UTRAN is evolving over time.
The UTRAN consists of a set of Radio Network Subsystems 128 (RNS), each of which has geographic coverage of a number of cells 110 (C), as can be seen in FIG. 1. The interface between the subsystems is called Iur. Each Radio Network Subsystem 128 (RNS) includes a Radio Network Controller 112 (RNC) and at least one Node B 114, each Node B having geographic coverage of at least one cell 110. As can be seen from FIG. 1, the interface between an RNC 112 and a Node B 114 is called Iub, and the Iub is hard-wired rather than being an air interface. For any Node B 114 there is only one RNC 112. A Node B 114 is responsible for radio transmission and reception to and from the UE 102 (Node B antennas can typically be seen atop towers or preferably at less visible locations). The RNC 112 has overall control of the logical resources of each Node B 114 within the RNS 128, and the RNC 112 is also responsible for handover decisions which entail switching a call from one cell to another or between radio channels in the same cell.
In UMTS radio networks, a UE can support multiple applications of different qualities of service running simultaneously. In the MAC layer, multiple logical channels can be multiplexed to a single transport channel. The transport channel can define how traffic from logical channels is processed and sent to the physical layer. The basic data unit exchanged between MAC and physical layer is called the Transport Block (TB). It is composed of an RLC PDU and a MAC header. During a period of time called the transmission time interval (TTI), several transport blocks and some other parameters are delivered to the physical layer.
Generally speaking, a prefix of the letter “E” in upper or lower case signifies the Long Term Evolution (LTE). The E-UTRAN consists of eNBs (E-UTRAN Node B), providing the E-UTRA user plane (RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs interface to the access gateway (aGW) via the S1, and are inter-connected via the X2.
An example of the E-UTRAN architecture is illustrated in FIG. 2. This example of E-UTRAN consists of eNBs, providing the E-UTRA user plane (RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are connected by means of the S1 interface to the EPC (evolved packet core), which is made out of Mobility Management Entities (MMEs) and/or gateways such as an access gateway (aGW). The S1 interface supports a many-to-many relation between MMEs and eNBs. Packet Data Convergence Protocol (PDCP) is located in an eNB.
In this example there exists an X2 interface between the eNBs that need to communicate with each other. For exceptional cases (e.g. inter-PLMN handover), LTE_ACTIVE inter-eNB mobility is supported by means of MME relocation via the S1 interface.
The eNB may host functions such as radio resource management (radio bearer control, radio admission control, connection mobility control, dynamic allocation of resources to UEs in both uplink and downlink), selection of a mobility management entity (MME) at UE attachment, scheduling and transmission of paging messages (originated from the MME), scheduling and transmission of broadcast information (originated from the MME or O&M), and measurement and measurement reporting configuration for mobility and scheduling. The MME may host functions such as the following: distribution of paging messages to the eNBs, security control, IP header compression and encryption of user data streams, termination of U-plane packets for paging reasons; switching of U-plane for support of UE mobility, idle state mobility control, System Architecture Evolution (SAE) bearer control, and ciphering and integrity protection of NAS signaling.
In mobile telecommunications, the two basic types of power control are open-loop and closed-loop. In open-loop power control (OLPC), a mobile terminal measures received pilot signal power and accordingly sets the transmission power density (PDS) according to this measured quantity, and based on the pilot transmitted power, the S(I)NR target, and the interference level (these last values are usually broadcasted by the base station). In closed-loop power control, the measurements are done on the other end of the connection, in the base station, and the results are then sent back to the mobile terminal so that the mobile terminal can adjust its transmission power. Note that the term “base station” is used broadly in this application, and may refer to a Node B, or an eNodeB, or the like.
The current trend in the art is that uplink power control will include: (i) an open loop power control mechanism at the terminal, as well as (ii) options for the eNode-B to send closed loop power control correction commands to the terminal. The current invention solves problems that occur with uplink power control and associated signalling from the terminal to the base station (eNode-B) to facilitate efficient uplink radio resource management decisions at the eNode-B.
Given this uplink power control scheme, the eNode-B may be unaware of the transmit power level at which different terminals are operating. This information is important for the eNode-B, because this knowledge is needed for optimal radio resource management decisions such as allocating MCS (modulation and coding scheme) and transmission bandwidth for the different terminals. It therefore has been discussed in 3GPP that terminals should be able to provide power control headroom reports to the eNode-B. The power control headroom report basically provides a measure of how close the terminal's power spectral density (PSD) is to the maximum PSD limit. The maximum PSD might be derived from the maximum UE transmit power (typically assumed to be on the order of 24 dBm) and the minimum bandwidth (typically 1 PRB).
Unfortunately, 3GPP has not yet been able to find satisfactory criteria for sending a power control headroom report from the user terminal to the eNode-B. In LTE uplink (UL), the eNode-B makes the scheduling and radio resource management decisions such as selecting the UEs to transmit, allocating the UE transmission bandwidths, and (as mentioned above) selecting the MCS they should use. These decisions are then signalled to the terminal(s) via dedicated signalling (e.g. UL scheduling grant message). And, in order to make these decisions properly, the eNode-B should be aware of the power level at which the terminals are transmitting, or some equivalent information like the power headroom information, since from this information the eNodeB derives which MCS can be supported in the future with a targeted block error rate (BLER) which would be otherwise not possible. Knowing at the eNode-B the power spectral density used by the mobile terminals is particularly important when selecting the transmission bandwidth (rather than the MCS). Not knowing with precision the PSD used by a mobile terminal when selecting the MCS has only a major impact in case of slow AMC (in which case the PSD is “automatically” increased/decreased when the MCS is modified).
Consequently, reporting of power headroom or some equivalent information is needed. However, reporting of the power control headroom is a trade-off between uplink signalling overhead versus performance improvements that result from having this information readily available at the eNode-B.
It is problematic to have the terminal periodically report the power control headroom at a frequency higher than the adjustments of the actual terminal power spectral density (PSD). Further, the aim of these power adjustments at the terminal is basically to (partly or fully) compensate the path-loss (including antenna-pattern, distance dependent path-loss and shadowing) between the eNode-B and the terminal, and the measurement of path-loss is done based on the DL (e.g. DL pilot channel). Even if the frequency of potential power adjustments at the terminal is high but the measured path-loss is not changing, UL signalling would be a waste of resources; the only issue then for reporting would be if closed loop power control commands would come from the eNodeB and some of those commands would be misinterpreted at the UE. Then, the problem occurs that the eNodeB does not know the used transmission power. The problem with power control commands being misinterpreted at the mobile terminal is only an issue if relative closed loop power control commands are used (which is also the working assumption in 3GPP).
In HSUPA, the UE Power Headroom (UPH) is part of the Scheduling Information (SI), which is transmitted by the UE as part of the MAC-e header. If the UE is not allocated resources for the transmission of scheduled-data, then Scheduling Information can be transmitted periodically and/or based on specific triggers (i.e. when data arrives in the buffer). Otherwise, only periodic reporting is supported.